1. Field of the Invention
This invention relates to a process for the production of low diamide content imidazolines, and their reaction with a quaternizing agent to form low-viscosity amphoteric surfactants.
2. Discussion of Related Art
U.S. Pat. No. 4,212,983 describes the production of a low diamide content imidazoline by heating of a crude imidazoline with an excess of aminoethyl ethanolamide through treatment of the reaction mixture in vacuo under reflux conditions.
The production of imidazoline-acrylate adducts is described in U.S. Pat. No. 3,555,041. The corresponding starting imidazolines are prepared by azeotropic reaction of fatty acid and amine.
U.S. Pat. No. 4,058,488 describes the production of imidazoline oxides, the starting imidazolines being prepared, inter alia, by azeotropic reaction. The corresponding amphoteric surfactants may be obtained from the imidazolines by reaction with a quaternizing agent.
U.S. Pat. No. 2,528,378 describes the reaction of equimolar quantities of imidazoline and chloroacetic acid in an aqueous solution of excess alkali. A solid mass is obtained.
Solid products are also obtained in accordance with U.S. Pat. No. 2,773,068, wherein an alkaline sodium chloroacetate solution is initially introduced into a reactor and imidazoline subsequently reacted with chloroacetic acid in the presence of an excess of sodium hydroxide, the chloroacetic acid being used in a two-fold excess.
Great Britain Pat. No. 850,514 describes the hydrolysis of imidazoline to the linear aminoamide which is reacted with sodium chloroacetate and mixed with ether sulfate. The specification thus describes the reaction of hydrolyzed imidazoline with sodium chloroacetate.
Products containing a high proportion of free chloroacetic acid are described in German patent application No. 20 63 424, equivalent to Great Britain Pat. No. 1,352,770. Imidazoline and chloroacetic acid are initially introduced, followed by the addition of sodium hydroxide at elevated temperature and at substantially neutral pH value.
Great Britain Pat. No. 930 296 describes the reaction of equimolar quantities of imidazoline and chloroacetic acid which is neutralized with a slight excess of sodium hydroxide. This reaction is carried out at 0.degree. to 15.degree. C. After heating to 95.degree. C., more sodium hydroxide is added. The reaction takes place in the presence of excess sodium hydroxide, giving carboxymethylation products based on a linear and branched aminoamide. The very low temperature at the beginning of the reaction is said to reduce the effect of the excess of sodium hydroxide on the ring cleavage.
European Pat. No. 1 006 describes the reaction of an imidazoline at 40.degree. to 90.degree. C. and at a pH of 7 to 11.5. When 0.5 mole of carboxymethylation substance has reacted, the pH value is raised to between 9 and 12. The reaction is controlled in accordance with the following general formula: EQU pH max.=[200-temp.(.degree.C.)]/13
This complicated process gives products containing more than 1% of free chloroacetic acid.
U.S. Pat. No. 4,269,730 in column 1 describes the reaction of imidazoline with neutralizing chloroacetic acid in the absence of strong alkali. In column 2, reference is made to the need to adhere strictly to the sequence, i.e. first reaction without alkali, then addition of alkali. According to the claims therein, 1 mole of imidazoline is heated at 70.degree. to 80.degree. C. with at least 1 mole of sodium chloroacetate in water (solids content 20 to 50%) until almost all the sodium chloroacetate has been consumed, after which an equivalent quantity of sodium hydroxide is added and the reaction mixture subsequently heated to 70.degree. to 80.degree. C. until the ring-opening reaction has started. Imidazoline and chloroacetate are reacted with one another in an elaborate, carefully controlled process in such a way that sodium chloroacetate is always present in excess. According to column 13 therein, the process requires a 92 to 99.5% imidazoline which is substantially free from starting methyl ester (0 to 2%) and which may only contain up to 5% aminoamide ("monoamide"); diamide contents are not mentioned.
European Pat. No. 40 346 describes a process for elimination of the diamine formed with the imidazoline which produces particularly persistant clouding in the final amphoteric surfactant. To destroy the diamide, the imidazoline is treated with an alkali before the reaction with sodium chloroacetate and is thus specifically converted into linear aminoamide. The resulting amphoteric surfactant is free from clouding, but is highly viscous.
An object of the present invention is to provide a new process for the production of highly concentrated, low-viscosity amphoteric surfactants which do not have any of the disadvantages mentioned above. This object is achieved by a quaternization process which starts out from low diamide content imidazolines and in which certain addition and temperature parameters are strictly observed.